Cellulose nanomaterial (CN) based waterborne polyurethane coating

1. A cellulose nanomaterial (CN) based waterborne polyurethane coating, wherein the polyurethane coating is a reaction product of a mixture consisting of CN, water, and at least one water-dispersible blocked polyisocyanate, wherein said CN is an active polyol, contributes at least 40-90 wt % of the total weight of the polyurethane coating, and comprises cellulose nanocrystals (CNC) or cellulose nanofibrils (CNF).

2. The CN based waterborne polyurethane coating of claim 1 , wherein the polyurethane coating is formed under an elevated temperature of 70-200° C.

3. The CN based waterborne polyurethane coating of claim 1 , wherein the polyurethane coating is formed through crosslinking reaction between hydroxyl groups of said CN and blocked isocyanate groups of the at least one water-dispersible blocked polyisocyanate, wherein said CN and the at least one water-dispersible blocked polyisocyanate are crosslinked through carbamate functional groups.

4. The CN based waterborne polyurethane coating of claim 1 , wherein the at least one water-dispersible blocked polyisocyanate is selected from the group consisting of diphenylmethane 4, 4′-diisocyanate (MDI) based water-dispersible blocked polyisocyanate, hexamethylene diisocyanate (HDI) based water-dispersible blocked polyisocyanate, bis(4-isocyanatocyclohexyl) methane based water-dispersible blocked polyisocyanate, isophorone diisocyanate (IPDI) based water-dispersible blocked polyisocyanate, toluene diisocyanate (TDI) based water-dispersible blocked polyisocyanate, and any combination thereof.

5. A method of preparing the cellulose nanomaterial (CN) based waterborne polyurethane coating of claim 1 , wherein the method consists of:

providing a CN aqueous suspension;

providing an aqueous suspension of at least one water-dispersible blocked polyisocyanate;

mixing the CN aqueous suspension and the aqueous suspension of at least one water-dispersible blocked polyisocyanate to provide a substantially homogenous mixture;

applying a layer of the substantially homogenous mixture to a substrate; and

curing the layer of the substantially homogenous mixture at an elevated temperature to provide the CN based waterborne polyurethane coating.

6. The method of claim 5 , wherein the substrate is a metal, glass, polymer, or ceramic material.